Nova analiza ντ → τ − → e − kanala u NOMADU

The NOMAD experiment at CERN is gathering its first data in the quest for neutrino oscillations, using the νµ wide band neutrino beam. The experiment is the most sensitive to oscillations νµ → ντ , but νµ → νe can be also studied as well as some additional physics. Here, the results of a novel study of the so-called “electronic channel”, i.e. ντ +N → τ − +X, followed by τ − → e −ντ ν¯e, is presented. The study is done with a help of a program based on the LEPTO event generator and simple detector simulation. It is shown that a conceivable deterioration of spatial resolution of the drift chambers with respect to what has been originally proposed, would not deteriorate significantly the signal-to-noise ratio in this channel. On the other hand, the quality of the φeh–φmh cut is shown to be extremely sensitive to the knowledge of the exact angle of incident neutrinos with respect to the horizontal axis of the detector. Finally, a new cut, involving the hadronic calorimeter installed at the back field return yoke of the NOMAD magnet, is proposed and shown to reduce the background by a factor of about two.Eksperiment NOMAD na CERNu prikuplja prve podatke u potrazi za neutrinskim oscilacijama, koristeći snop mionskih neutrina širokog energijskog spektra. Eksperiment je najosjetljiviji na oscilacije νµ → ντ , ali mogu se također detektirati i oscilacije νµ → νe, te studirati dodatna fizika. Ovdje dajemo prikaz rezultata nove studije tzv. “elektronskog kanala”, tj. νµ + N → τ − + X nakon čega slijedi τ − → e −ντ νe. Studija je sačinjena uz pomoć programa baziranog na LEPTO generatoru događaja i jednostavnoj simulaciji detektora. Pokazano je da moguća slabija prostorna rezolucija driftnih komora od one razmatrane u prvotnom prijedlogu samo marginalno utječe na omjer signal/šum u tom kanalu. S druge strane, kvaliteta φeh–φmh reza je izrazito osjetljiva na precizno poznavanje upadnog kuta neutrina s obzirom na horizontalnu os detektora. Konačno, pokazano je da dodatni rez, koji uključuje hadronski kalorimetar koji je instaliran straga u željeznoj jezgri elektromagneta, reducira pozadinu za otprilike faktor dva